A common step in producing printed products using web offset printing press technology includes forming, folding and cutting a continuous paper web to form printed products, referred to as signatures. According to a conventional production method, the signatures exit from a folder apparatus after being processed by, for example, a fan wheel or deceleration device, which slows the speed of the signatures relative to the speed of the web. An example of such a deceleration device is described, for example, in U.S. Pat. No. 5,452,866. The signatures generally exit the folder for further processing on a conveyor in imbricated (e.g., shingled) fashion and in ordered series. It is important to maintain the ordering, or registration, of the signatures because the further processing typically involves combining multiple signatures, by binding or other means, to create a final product.
In web-offset printing, the image to be transferred onto the paper web is typically etched onto a printing plate mounted on a print cylinder. The ink image is transferred from the plate cylinder onto a blanket cylinder which then transfers the image onto the paper web. If, for example, the width of the printed image is less than one half the circumference of the print cylinder, multiple images can be printed with one rotation of the print cylinder. Accordingly, two separate products can be printed simultaneously onto a single web, which results in signatures for the first product exiting from the folder nested between signatures for the second product in a single imbricated stream. Thus, before the signatures can be further processed, it is desirable to separate the two signature versions without loss of registration.
U.S. Pat. No. 4,550,822 describes an apparatus for transporting flat products, especially printed products arriving in an imbricated formation. Each gripping unit of the apparatus comprises a stationary clamping jaw, a pivotable clamping jaw and a plate shaped stop. The pivotable clamping jaw is pivoted against the action of a closing spring by a cam structure or the like. The products are first accelerated and then pushed into the open gripper mouth until abutting the stop. Thereby, the printed products are aligned at the region of their leading edges. At their trailing edges the printed products remain under the conveying action of the belt conveyor at least until the gripper units are closed.
U.S. Pat. No. 4,072,228 describes an apparatus for evening an imbricated stream of printed products. This apparatus comprises a number of revolving entrainment members designed to engage the printed products and which are in a drag connection with one another. The entrainment members are driven by a thrust drive at the beginning of their conveying action path and by a traction drive at the end thereof. After the entrainment members engage the printed products, the thrust and traction drives cause a change in the spacing of the entrainment members and, consequently, in the spacing of the products.
U.S. Pat. No. 3,809,214 describes a turning conveyor for flat structures, especially printed products. This turning conveyor encompasses a plurality of entrainment members which move along with the flat structures. Each entrainment member can be brought into engagement with a respective one of the flat structures. The entrainment members are controlled such that, at least at the time they are in engagement with a flat structure, they turn relative to the direction of movement of the main conveyor, thereby turning the flat structures during the course of conveying same about an axis which is perpendicular to the flat structures.
Another known method of separating a stream of products uses a gripper conveyor system and a vacuum belt, such as are commonly used with newspaper gripper conveyor systems. In such a conventional gripper conveyor system, the gripper blocks are connected to one another, similar to links in a chain, and the gripper blocks form the conveyor cable. For example, such a gripper conveyor drags a stream of products over a vacuum belt traveling slower than the conveyor and releases every second flat product from the gripper conveyor onto the vacuum belt. This method of separating a stream of products has the disadvantage that it does not allow positive control of the signatures while separating them from a primary product stream to secondary product streams. More particularly, this method relies on the attractive force between the vacuum belt and the trailing edge of the released signature to maintain orientation of the signature. This degree of control is insufficient at high speeds or when transporting light products.
Therefore, with the foregoing in mind, it is a primary object of the present invention to provide a new and improved method and apparatus for separating two or more versions of flat structures, especially printed signatures, arriving from a folder in a single imbricated stream into two or more secondary streams without the loss of registration between the adjacent streams.
A further object of the present invention is to perform the separating of the signatures while maintaining positive control of the flat structures as they exit the folder, thereby maintaining reliability at high speeds and with light products.